Failures: Rules of (gasket) engagement

by arslan_ahmed | June 8, 2023 4:05 pm

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Preformed gaskets are commonly used to secure glazing and reduce water penetration—and in some instances air flow—through joints in exterior wall assemblies due to their relative consistency, ease of installation, and long-term serviceability. Effective gasket design should consider project-specific variables, such as installation accessibility, construction tolerances, compression forces, and in-service joint movement. Preformed gaskets should also be designed with some mechanism to prevent disengagement over time, such as an integral dart, a locking barb, and/or the application of an appropriate adhesive. Often, project variables will also determine the appropriate mechanism for gasket retention. Gaskets are typically pre-set or wedge type, and verifying proper installation of a wedge gasket can be challenging given the engagement mechanism between gasket and substrate components is typically concealed.

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A wedge gasket has a tapered profile, often incorporating a locking barb (which engages into a recessed groove or raceway within the joint), that is designed to be driven into a fixed dimension joint between two adjacent enclosure components. If the locking barb is not fully engaged, the wedge gasket relies on its stiffness and friction to maintain compression between adjacent components which can lead to disengagement over time. Gasket stiffness is determined by its material hardness (i.e. durometer) and profile (i.e. solid versus hollow). Solid wedge gaskets would be comparatively stiff with little capacity for movement, compared to an extrusion profile that has internal voids. Most gasket materials do not always return to their original profile dimensions after being compressed for an extended period and then released (e.g. when a wedge gasket backs out of a static joint).

On a recent high-rise project, wedge gaskets were used as part of a unitized curtain wall system to prevent projecting trim components from rotating or detaching. Following several years of occupancy, the building maintenance team identified an increase in localized and complete disengagement of wedge gaskets, particularly on higher floors of the south- and east-facing elevations during winter months. A close-range examination revealed the gaskets were not driven to the required depth within the joints to engage the locking barb with the corresponding raceway in the outboard aluminum trim. Instead, they were retained in the joint through compression alone, leaving them susceptible to disengagement over time. Inadequately engaged gaskets were found to be particularly vulnerable on elevation areas that received direct sun exposure during winter months due to increased movement and dimensional changes of the outboard components from the more extreme thermal cycling created by colder ambient conditions and solar radiation.

During the close-range examination, inadequately engaged gaskets were able to be removed without much resistance. It was further determined that reinserting the same gasket into the joint at the intended depth, so the locking barb was fully engaged in the trim raceway, resulted in an installation that could not be easily removed using the same evaluation procedures. The lack of visual difference between the original and re-driven gasket installation emphasizes the need for the system installer to be more cognizant of the gasket design and its proper installation. Further, protocols should have been established as part of a quality assurance program to periodically test in-place gaskets to verify their proper engagement.

Authors

Jeffrey Sutterlin, PE, is an architectural engineer and associate principal with Wiss, Janney, Elstner Associates’ (WJE’s) office in Princeton, New Jersey. He specializes in investigation and repair of the building envelope. Sutterlin can be reached at jsutterlin@wje.com.

David S. Patterson, AIA, is an architect and senior principal with Wiss, Janney, Elstner Associates’ (WJE’s) office in Princeton, New Jersey. He specializes in investigation and repair of the building envelope. Patterson can be reached at dpatterson@wje.com.

The opinions expressed in Failures are based on the authors’ experiences and do not necessarily reflect that of The Construction Specifier or CSI.

Source URL: https://www.constructionspecifier.com/failures-rules-of-gasket-engagement/

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